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In United States patent law, the machine-or-transformation test is a test of patent eligibility under which a claim to a process qualifies to be considered for patenting if it (1) is implemented with a particular machine, that is, one specifically devised and adapted to carry out the process in a way that is not concededly conventional and is not trivial; or else (2) transforms an article from one thing or state to another.
The test has been articulated recently in In re Bilski, but dates back to the nineteenth century. The test is articulated also in the patent-eligibility trilogy—Gottschalk v. Benson, Parker v. Flook, and Diamond v. Diehr.
Supreme Court has held that this is not the only test 
The Supreme Court has held that the machine-or-transformation test is not the sole test for the patent-eligibility of processes. The certiorari petition in Bilski challenges that proposition. In Gottschalk v. Benson, the Court expressly reversed the Federal Circuit on this point, stating:
It is argued that a process patent must either be tied to a particular machine or apparatus or must operate to change articles or materials to a “different state or thing.” We do not hold that no process patent could ever qualify if it did not meet the requirements of our prior precedents.
The government had made an argument in its brief in Benson that the Court should so hold and that it was impossible to rationalize the case law any other way. The Court, in its ruling, refused or failed to agree with that argument.
Outstanding issues 
The Benson and Bilski opinions left important details of the machine-or-transformation test unexplained. The details include what kind of transformation is sufficient to confer patent-eligibility and what are the characteristics of a "particular machine" that confers patent-eligibility.
Transformation of an article from one thing or state to another is said to be a clue to patent-eligibility. Thus, in Benson, the Court stated, "Transformation and reduction of an article `to a different state or thing' is the clue to the patentability of a process claim...." A hundred years earlier, the Court had said, “A process is ... an act, or a series of acts, performed upon the subject matter to be transformed and reduced to a different state or thing."
What is an article? 
The Benson opinion indicated that the article had to be a physical object, such as a lump of rubber (to be transformed from raw to cured state), a piece of leather (to be transformed from untanned skin to tanned leather), or a pile of flour (to be transformed from coarse to superfine particles). The Federal Circuit’s In re Schrader opinion, however, indicated that the article could be an electronic signal representative of a physical parameter, such as an EKG (“electrocardiograph signals representative of human cardiac activity “) or seismogram (“seismic reflection signals representative of discontinuities below the earth's surface”) signal. Thus, the Schrader opinion chided the Supreme Court for speaking of physical “articles” rather than “subject matter,” and thus only “imperfectly” reflecting the relevant legal principle. The Bilski court appears to adhere to the Schrader formulation, rather than that of Benson, so that it seems to consider a signal transformation patent-eligible when the signal is representative of certain types of physical actions. But a transformation of signals representative of monetary or legal relations does not qualify, given the affirmance of the PTO’s rejection of Bilski’s claim and perhaps the Bilski court's treatment of State Street Bank, as well.
How much of a transformation is needed? 
Judge Rader asked in his Bilski dissent, “What form or amount of ‘transformation’ suffices?” The court did not answer his question. It may be that a “substantial” physical or chemical change of properties that is material to the objectives of the invention is required, but this is still to be resolved.
A “particular machine” 
Benson and Bilski speak of the process being tied to “a particular machine” while Flook says that the mechanical implementation of a natural principle must be “inventive”:
Even though a phenomenon of nature or mathematical formula may be well known, an inventive application of the principle may be patented. Conversely, the discovery of such a phenomenon cannot support a patent unless there is some other inventive concept in its application.
In Flook the implementation was conceded to be conventional and no departure from the prior art. Therefore, the principle with or plus a conventional implementation was patent-ineligible. The Flook Court also cited and relied on the same principle as being illustrated in Funk Brothers Seed Co. v. Kalo Inoculant Co., in which the natural principle was implemented in a manner so trivial on its face that the patent on the implementing article of manufacture was tantamount to a patent on the natural principle.
This aspect of the machine-or-transformation test remains an uncertain and controversial issue, as it remains "unclear whether tying a process to a general purpose computer is sufficient to pass the machine-or-transformation test" and it has not been authoritatively determined whether use of the "programmed computer claim format" overcomes the patent-eligibility problem. The Federal Circuit's Bilski opinion explicitly left the question unresolved. In the opening words of the Benson opinion, however, this statement occurs:
Respondents filed in the Patent Office an application for an invention which was described as being related "to the processing of data by program and more particularly to the programmed conversion of numerical information" in general purpose digital computers. ...The claims were not limited to any particular art or technology, to any particular apparatus or machinery, or to any particular end use. They purported to cover any use of the claimed method in a general purpose digital computer of any type.
Arguably, this language disposes of the issue. Some pre- and post-Bilski decisions of the PTO appellate board (BPAI) take the position that a programmed general-purpose digital computer is not a “particular machine,” and that corresponding Beauregard claims to an encoded medium are equally nonstatutory.
In CyberSource Corp. v. Retail Decisions, Inc., a California federal district court held that limitation of a process to implementation "over the Internet" does not satisfy the machine-or-transformation test. First, the Internet is not a "particular machine." The Internet is an intangible abstraction. Second, the limitation to a particular technological environment is a mere field-of-use limitation, which does not suffice under sec. 101. Third, the use of the Internet does not impose meaningful limits on the preemptive scope of the claims. The same court held that a "Beauregard" claim directed to the instructions for performing a method that does not pass the machine-or-transformation test will also fail to pass that test. The court pointed out that the PTO appellate board had similarly interpreted Bilski.
Another imperfectly resolved issue is whether the machine-or-transformation test is narrowly misnamed, since the relevant case law includes comparable implementations of natural-principle processes with other types of physical object besides a machine. In Funk, on which Flook relied, the implementation of the natural principle was with a package — an article of manufacture. There is no principled reason why a natural-principle process must be implemented physically with a machine and not with an article of manufacture or composition of matter. The test explained in Bilski thus should be regarded as a physical object or transformation test or a device-or-transformation test.
Is satisfying the test a necessary condition for patent-eligibility, a sufficient condition, both or neither? 
It is debatable whether In re Bilski makes the machine-or-transformation test a necessary condition for patent-eligibility, a sufficient condition, or both a necessary and sufficient condition. The Bilski opinion seems to declare a rule that a claimed invention is patent-eligible if and only if it satisfies the machine-or-transformation test. Both prongs of if-and-only-if have been challenged.
An example illustrating the proposition that satisfying the machine-or-transformation test is not a sufficient condition for patent-eligibility occurs in U.S. Pat. No. 6,701,872. This patent covers a method and apparatus (machine) for entertaining a cat by using a moving laser beam (relatively high technology). The method is implemented with a “particular machine”—“a rotating laser source mounted directly on a shaft driven directly by a motor mounted on a portable pedestal” (method claim 14). But it is debatable whether entertaining a cat may be considered a useful Art, and some may argue that this “discovery” is not the kind of discovery that the Patent Clause contemplates.
Attempts have been made, also, to describe processes that fail to satisfy the machine-or-transformation test but nonetheless seem clearly to be patent-eligible.
A method of removing dirt from a soiled garment, comprising:
placing a soiled garment in flowing water; and
shaking said garment for at least five minutes.
The question has been raised, also, whether beating the garment with a stick constitutes use of a "particular machine." That question is illustrated by the following hypothetical claim that is a variation on the preceding example:
A method of removing dirt from a soiled garment, comprising:
submerging a soiled garment in water; and
beating said garment for at least five minutes with a stick.
The point of this type of analysis is that the machine-or-transformation test does not work for all cases. There are some unusual outliers that satisfy the test but are patent-ineligible and some that do not satisfy the test but are patent-eligible.
The "corollaries" 
Bilski points out, and the PTO recently emphasized in a memorandum to its Examining Staff, that there are two "corollaries" to the machine-or-transformation test. First, a mere field-of-use limitation is generally insufficient to make an otherwise ineligible method claim patent-eligible. The PTO Guidance Memo explains that “[t]his means the machine or transformation must impose meaningful limits on the method claim's scope [for it] to pass the test.” What makes a limitation meaningful is unstated, but perhaps that concept can be defined in terms of whether the limitation places only an insubstantial limitation on claim scope or preemptiveness.
The second corollary is that insignificant extra-solution activity will not transform an unpatentable principle into a patentable process. The PTO Guidance Memo explains that “[t]his means reciting a specific machine or a particular transformation of a specific article in an insignificant step, such a data gathering or outputting, is not sufficient to pass the test.” It is unclear whether this concept would apply to such acts as gathering temperature data from thermocouples inside a mold or opening the lid of a mold upon the completion of a curing process.
It is reasonable to assume that whether a given step is insignificant or central to a claimed process will be a controversial issue in post-Bilski cases testing the meaning of the machine-or-transformation test.
Possible interaction between the machine-or-transformation test and the exhausted combination doctrine 
It has not yet been explored in litigation whether claiming a computer-related advance as an exhausted combination provides a way to prevent the claimed advance from being classified as nonstatutory subject matter. A so-called exhausted combination claim is one to a device in which a novel group of elements cooperates in a conventional manner with some old elements—for example, a new kind of motor and an old disk drive. Placing a process that fails the machine-or-transformation test in a machine environment overcomes the absence of implementation by a specific machine, as required by In re Bilski and the Supreme Court decisions on which it is based.
The format of the processes claimed in Diamond v. Diehr, Parker v. Flook, and Gottschalk v. Benson illustrate the concept and its practical application. In Diehr, the claim was to “a method of operating a rubber-molding press” using the Arrhenius equation, and the claim contained at least minimal references to the mold press and other apparatus. The Court held the claim patent-eligible. In Flook, the claim was to a "method for updating the value of at least one alarm limit," where an “’alarm limit’ was a number.” The claim said nothing about a chemical reaction vessel or even temperature measuring devices. The Court held the claim patent-ineligible. In Benson, the claim was to “a data processing method for converting binary coded decimal number representations into binary number representations.” One claim mentioned a reentrant shift register and the other claim mentioned no apparatus at all. The Court held both claims patent-ineligible, however, on the ground that the computer-equipment limitation was too trivial to avoid preempting the idea, since the method could not feasibly be used except with a computer.
In Flook, the claim could have instead been to “a method of operating a hydrocracking plant wherein hydrocarbon feedstock is fed into a chemical reactor, heat is applied, etc.” The claim, although to an exhausted combination, would have required apparatus as did that in the Diehr case. Similarly, the claim in Benson could have been to a method of operating a telephone switch box or perhaps even a method of providing binary-coded-decimal numerical signals to a binary-coded operating device. Again, by providing a seemingly nontrivial mechanical environment, even though it was just an exhausted combination, the claims drafter might have avoided the holding of nonstatutory subject matter (patent-ineligibility). It is thus possible that careful claims drafting techniques will succeed in elevating form over substance, to avoid the impact of the machine-or-transformation test.
- Stefania Fusco, "Is In re Bilski a Deja Vu?", 2009 Stan. Tech. L. Rev. P1
- 545 F.3d 943 (Fed. Cir. 2008). See also In re Ferguson, 558 F.3d 1359 (Fed. Cir. 2009).
- The Benson opinion explains several examples. In Corning v. Burden, 56 U.S. (15 How.) 252 252 (1853), the Court said, “One may discover a new and useful improvement in the process of tanning, dyeing, etc., irrespective of any particular form of machinery or mechanical device.” Id. at 267-68. The Benson Court explained that the illustrative processes in Corning — “the arts of tanning, dyeing, making waterproof cloth, vulcanizing India rubber, smelting ores”—are instance where “the use of chemical substances or physical acts, such as temperature control, changes articles or materials. The chemical process or the physical acts which transform the raw material are, however, sufficiently definite to confine the patent monopoly within rather definite bounds.” Benson, 409 U.S. at 69. In Cochrane v. Deener, 94 U. S. 780 (1876), the Court upheld a patent on a process for manufacturing “superfine” flour, although the claim was not limited to any particular form of machinery. Such a process “is a mode of treatment of certain materials to produce a given result. It is an act, or a series of acts, performed upon the subject matter to be transformed and reduced to a different state or thing.” Id. at 788. The Benson Court also explained Tilghman v. Proctor, 102 U. S. 707 (1880), as a case in which the process transformed fat into glycerin by uniting a water molecule with a fat molecule. Benson, 409 U.S. at 70.
- 409 U.S. 63 (1972).
- 437 U.S. 584 (1978).
- 450 U.S. 175 (1981).
-  Supreme Court Opinion
- See Bilski petition at 16-21.
- 409 U.S. at 71.
- See Petitioner’s Reply Brief on writ of certiorari in Benson, at 9 (“we submit that the cases follow such a rule –– implicitly or explicitly –– and that they cannot be rationalized otherwise”).
- Cochrane v. Deener, 94 U.S. 780, 787-788 (1877).
- As Benson explains, the vulcanization of rubber and tanning of leather are examples of processes that can be carried out "irrespective of any particular form of machinery or mechanical device," according to the decision in O’Reilly v. Morse, 56 U.S. (15 How.) 62 (1853). See Benson, 409 U.S. at 69.
- As Benson explains, Cochrane "involved a process for manufacturing flour so as to improve its quality. The process first separated the superfine flour and then removed impurities from the middlings by blasts of air, reground the middlings, and then combined the product with the superfine." Benson, 409 U.S. at 69.
- 22 F.3d 290 (Fed. Cir. 1994).
- As the Bilski court explained, “legal obligations, organizational relationships, and business risks” are just “abstract constructs.” See Bilski, 545 F.3d at 962.
- 437 U.S. at 594. See also Ansonia Brass & Copper Co. v. Elec. Supply Co., 144 U.S. 11, 18 (1892) ("The application of an old process or machine to a similar or analogous subject, with no change in the manner of application and no result substantially distinct in its nature, will not sustain a patent even if the new form of result had not before been contemplated. ...On the other hand, if an old device or process be put to a new use, which is not analogous to the old one, and the adaptation of such process to the new use is of such a character as to require the exercise of inventive skill to produce it, such new use will not be denied the merit of patentability.").
- 333 U.S. 127 (1948).
- The inventor discovered desirable properties of certain bacteria and claimed as an invention a package consisting of the bacterial material put into a container in order to sell it.
- This claim format relies on the legal doctrine that a new program makes an old general purpose digital computer into a new and different machine. The issue is discussed in the article--the Old Piano Roll Blues (analogizing the argument to saying that putting a new piano roll into an old player piano turns the latter into a new machine).
- The Bilski opinion said: "We leave to future cases the elaboration of the precise contours of machine implementation, as well as the answers to particular questions, such as whether or when recitation of a computer suffices to tie a process claim to a particular machine."
- Benson, 409 U.S. at 64. Accord Dann v. Johnston, 425 U.S. 219, 224 (1976).
- Judge Rich so opined in his dissenting opinion in In re Chatfield, 545 F.2d 152, 161 (Ct. Cus. & Pat. App. 1976) , cert. denied as untimely filed, 434 U.S. 875 (1977) ("I have turned to the competing contentions which were presented to the Supreme Court in Benson, to its decision that we erred in holding the claims statutory, which was our only holding, and have concluded that the members of the Court participating in that decision were unanimous in holding that programs for general-purpose digital computers, at least when claimed as a 'process,' are not within the meaning of that category of inventions in the statute. It is my own view that claiming as a 'machine'” instead of as a 'process' is no distinction at all because it is merely a drafter's choice.").
- See, e.g., Ex parte Mitchell (BPAI 2009)(“We see no reason why a ‘computer readable medium’ containing ‘instructions’ for the otherwise ineligible method should be treated any differently from the non-statutory method recited in [method] claim 1.”); Ex parte Cornea-Hasegan (BPAI 2009) (“[T]he recitation of a processor does not limit the process steps to any specific machine or apparatus.”); id. (“Limiting the claim to computer readable media does not add any practical limitation to the scope of the claim."); Ex Parte Halligan (BPAI 2008); Ex parte Wasynczuk (BPAI 2008).
- -- F. Supp. --, 2009 WL 815448 (N.D. Cal Mar. 23, 2009).
- See Ex parte Cornea-Hasegan, 89 U.S.P.Q.2d 1557, 1561 (B.P.A.I. 2009).
- In Armour Pharmaceutical Co. v. Richardson Merrell, Inc., 396 F.2d 70, 74 (3d Cir. 1968), the natural principle was implemented by coating trypsin with an enteric coating to protect it from stomach acid — a facially-trivial expedient. The implementation was either a composition of matter or an article of manufacture. In Neilson v. Harford,  151 ER 1266, patent-eligibility was based on the presence of a "receptacle," i.e., a metal box, to which heat was applied. The court said, "In this receptacle he directs the air to be heated by the application of heat externally to the receptacle," in order to implement the principle of the invention. This apparatus would appear to be an article of manufacture, rather than a machine, since it lacks interacting parts.
- The "useful Arts" requirement differs from the machine-or-transformation test in purpose and substance, in that the "useful Arts" requirement considers the kind of human endeavor on which a patent is sought, to exclude certain categories of endeavor, while the machine-or-transformation test seeks to filter out advances in thinking that are claimed so broadly and/or abstractly that they excessively preempt large fields of endeavor in a manner that risks hindering the progress of useful Arts. The latter test differs also in being instrumental and in no sense important in itself as a policy.
- Case-Law Developments After State Street and AT&T (viewed Mar. 25, 2009).
- Id. See also accompanying illustration.
- Guidance for Examining Process Claims in view of In re Bilski ("Guidance Memo").
- The Supreme Court so held in Flook, where the claim’s limitation to use in a hydrocracking process was ineffective to confer patent-eligibility. Moreover, in Diehr, the Court stated that ineligibility under § 101 "cannot be circumvented by attempting to limit the use of the formula to a particular technological environment." 450 U.S. at 190-91.
- This principle is also supported in Diehr and Flook. The Diehr Court said that "insignificant postsolution activity will not transform an unpatentable principle into a patentable process." 450 U.S. at 191-92. See also Flook, 437 U.S. at 590 ("The notion that post-solution activity, no matter how conventional or obvious in itself, can transform an unpatentable principle into a patentable process exalts form over substance.").
- See Minebea Co. v. Papst, 444 F. Supp. 2d 68 (D.D.C. 2006).
- This expedient was suggested initially in Richard H. Stern, Tales From the Algorithm War, 18 AIPLA Q.J. 371 (1991).
- The Court’s opinion states that it was conceded that the process was known and conventional except for its use of the algorithm.